Electrophotographic flash system

ABSTRACT

A flash system for an electrophotographic reproduction apparatus is provided comprising a flash exposure station, a flash fusing station, a flash power supply, and control circuit means for utilizing the power supply for energizing both the exposure and fusing stations on a time-shared basis. The power supply is sized to furnish sufficient power for exposure with a single flash and for fusing an entire copy sheet with multiple flashes, preferably with each flash fusing a separate section of the copy sheet at a time.

United States Patent 11 1 Mabrouk 1 Mar. 18, 1975 1 1 ELECTROPHOTOGRAPHIC FLASH SYSTEM [75] Inventor: Saied Abd-Elrahman Mabrouk,

Cleveland Heights, Ohio [73] Assignee: Addressograph-Multigraph Corporation, Cleveland, Ohio [22] Filed: Dec. 3, 1973 [21] Appl. No.: 421,122

52 us. c1 355/11, 219/216, 315/183, 315/241 P, 355/14 51 1111.01 G03g 15/22 [58] Field of Search 355/3 R, 11, l4;219/2l6, 219/388; 117/21; 315/178, 182, 133, 241 P,

[56] References Cited UNITED STATES PATENTS 2,894.174 7/1959 Schankler....; 315/230 Michaels 219/388 X Zoppoth 355/3 R Primary ExaminerSamuel S. Matthews Assistant Examiner--Kenneth C. Hutchison Attorney, Agent, or Firm--Harry M. Fleck, Jr.

[57] ABSTRACT 15 Claims, 4 Drawing Figures 1 ELECTROPHOTOGRAPHIC FLASH SYSTEM The present invention is generally related to electrophotography and, more particularly, to an improved flash system for exposure and fusing.

In recent years, the use of flash lamps, such as the xenon type, for flash exposure in electrophotographic equipment has become quite common. Due to its high speed capabilities, flash lamps have also been utilized successfully for toner image fusing. Typically, to provide the desired flash for either exposure or fusing, a high DC. voltage source is utilized to charge a capacitor and a triggering circuit is provided to initiate energization of the flash lamp. The DC. source and capacitor must be capable of supplying sufficient energy to carry out the flash operation Typically, the energy required to irradiate a 8 X 11 inch or 8 k X 14 inch original document with xenon flash for exposure of a photoconductor is in the range of 150-250 joules. For xenon typeflash fusing of an image pattern on the same size of a plain paper copy material, 500 to 800 joules is normally required. As such, copier machines utilizing flash type exposure required a D.C. supply and storage capacitor which together occupied a considerable amount of machine space. Conventional machines with single flash type fusing required even larger power supplies which were bulky, heavy, and more particularly, costly to manufacture. These factors were of even greater significance with machines utilizing flash for both exposure and fusing, such machines requiring two D.C. supplies, two control circuits, and approximately 120 and 50 microfarad capacitances for fusing and exposure, respectively. It is apparent that such dual components'presents a significant cost factor of the overall copier machine.

It is a primary object of the present invention to provide a versatile flash system, preferably with xenon type flash lamps, which overcomes the above-mentioned shortcomings of conventional machines utilizing flash fusing and/or flash exposure.

It is another object of the present invention to provide a novel electrophotographic reproduction apparatus including means for both flash exposure and flash fusing with a common power supply utilized on a timeshared basis.

It is a further object of the present invention to provide a unique flash power supply and control circuit for image fusing on a copy sheet by producing several flashes, each of considerably less energy than the energy required to fuse an entire sheet with a single flash, whereby the flash power supply is considerably smaller and less costly than conventional flash power supplies.

Yet another object of the present invention is to provide a highly versatile flash system which is of relatively simple construction and which is relatively inexpensive to manufacture and maintain, compared with conventional flash systems.

Other objects and advantages of the present invention will become apparent from the following detailed description thereof made with reference to the ac'com panying drawings wherein:

FIG. 1 is a block diagram of the flash system of the present invention.

FIG. 1a is a diagrammatic illustration of the sectional fusing arrangement associated with the present invention.

FIG. 2 is a timing diagram of the control signals and their relation to the fusing and exposure flash operations of the flash system of the present invention.

FIG. 3 is a schematic-diagram of a preferred embodiment of the circuitry associated with the present invention.

Referring now, more particularly, to FIG. 1 of the drawings, the flash system of the present invention is generally indicated by the numeral 10 and includes a flash exposure station 12 and a flash fusing station I4. Preferably, the exposure station is of a conventional type and includes a pair offlash lamps l6 and 18, which are appropriately energized, as hereinafter explained, to irradiate an original document to be copied. The radiation reflected from the original document is used to expose a light sensitive surface, such as a photoconductor, which provides a latent image pattern which is subsequently developed by the application of toner particles. Various techniques of exposure and development are well known to those skilled in the art of electrophotography and a detailed description of such is deemed unnecessary for this disclosure. It will be appreciated that the flash system, hereinafter described, is not lim ited to use with any particular type of electrophotographic reproduction apparatus and may be utilized with both plain and coated paper systems and with various types of developers and toners.

Fuser station 14 is provided with a flash lamp 20 which is mounted in the cavity or interior ofa radiation reflector 22, which is appropriately shapedto provide relatively uniform radiation over reflector opening area 23 which overlies a sheet of copy material 24. Preferably, reflector 22 is sized and shaped such that each fusing flash irradiates only a section of a copy sheet at a time. The copy sheet is advanced by a conventional transport or motive means generally indicated by the numeral 26, whereby the entire copy sheet eventually passes beneath fuser 14. This arrangement is illustrated in FIG. la.

It will be appreciated that the energy required to achieve satisfactory fusing of the toner particles to the copy material is a function of the amount of toner to be fused which is generally related to the total surface area of the copy material. In typical xenon flash fusing processes involving plain paper copy sheet, 8 k X l l to 8 /z X 14 inches in size, approximately 500 to 800 joules of energy is required. Larger copy sheets normally require even more energy for satisfactory fusing. As mentioned above, with conventional machines utilizing single flash fusing, it was necessary to provide a relatively large and costly'power supply to produce sufficient flash energy for satisfactory fusing. The flash system of the present invention is capable of providing fusing by multiple flashes, whereby the energy of each flash is only a fraction of the total energy normally required to fuse an entire copy sheet. As such, the size and cost of the power supply required for fusing is significantly less than that of conventional power supplies for flash fusmg.

As illustrated in FIG. la, the fuser reflector 22 is sized such that it irradiates only a half of the copy sheet at a time. The control circuitry, as hereinafter explained, provides energization of the fuser flash lamp 20 when the first section 24a of the copy sheet underlies reflector 22. When section 24b is brought into alignment with reflector 22, the control circuit effects a second energization of flash lamp 20 to fuse the toner particles to section 24b of twoflash fusin'g ofthe copy sheet,'the energy per flash is only half that required if the entire sheet was fused with a single flash-Of course, it is not intended that the present invention be limited to the use of two flashes, and-a greater number of flashes may be provided if larger-copy sheets arebeing handled or if such will permit further reduction-in the sizeof the system power supply..ltwill,al so beappreciated thatradiation of the different copy sheet-sections maybe accommodated by moying'the fuser from one section to another, if it is feasible tocdogso. Preferably; theiflash system of the present invention-utilizes well known xenon type flash lamps, although-it is not intended that the invention be limited to xenon, as other types of flash lamps may be utilized, ifdesirable. Typically, the pulse width for each fuse flash is 300-400 microseconds. Since each fuse flash is nearly instantaneous in nature, it is unnecessary to stop .thecopy material to fuse each section. Preferably, the fuser reflector is slightly wider than a copy sheet section, say by one-eighth to one-fourth inch, to

assure that there are no unfused areas or gaps between each section.

Energy for both fusing and exposure is provided by a storage capacitor and a pair of trigger transformers generally indicated by block 28 in FIG. 1. Prior to each exposure or fuse flash, the storage capacitor is charged by way 'ofa D.C. source including a charging transformer and rectifier, generally indicated by block 30. The exposure and fuse flashes are initiated by a triggering circuit 32 in'response to signals received from a main control circuit 34. Various command signals are provided to main control circuit 34 from an appropriate logic circuit not illustrated. Preferably, these command signals include exposure pre-charge, exposure trigger, fuse p're-charge, and fuse trigger. The main control circuit is effective to connect the D.C. voltage source 30'tothe storage capacitor in response to either the exposure or fuse pre-charge command signals. When the'charge of the storage capacitor reaches the predetermined level, control circuit 34 is effective to disconnect D.C. source 30 from the storage capacitor.

It will be appreciated that the charging system illustrated in FIG". l-provides energization of the exposure and fu'singflash lamps from a common storage capacitor charged ,bya common power supply. The trigger and'pre cha'rge command signals to control circuit 34 occur in an arrangement such that the exposure and fuse operations are alternated. Thus, the storage capacitor and D.CL voltage source define a flash power supply'which is time-shared between the exposure and fusing-stations. ln order to provide optimum utilization of the power supply, the flash fuse energy should be 'nearly'equ'algto' the flash exposure energy. As mentioned above, in atypical application the energy required-'forfexposure is 150-250 joules and the energy required forflash fusing is 500-800joules. By providing two fuse flashes for each'exposure flash, the energy requiredp'er fuse flash in a typical application would range-from .250to 400..joules. Depending upon the 'ekactfusing-power requirementsand the fusing cavity the copy sheet. By providing 7 by an exposure pre-charge command signal pulse 36 from the logic circuit. Typically, this signal pulse is approximately 20 milliseconds in width and is effective to initiate charging of the'capacitor. The'storage capacitor voltage increases as indicated at 37 until it reaches a predetermined level 38, at which time charging is terminated. An exposure trigger command signal 39 is subsequently received from the logic circuit which initiates energization of the exposure flash lamp, which discharges the storage capacitor. Discharge of the exposure'lamp is nearly instantaneous and is indicated by the vertical line at 40. The discharge is followed shortly thereafter by a fuser pre-charge command signal 42 which causes'recharging of the storage capacitor for fusing purposes as indicated by sloped line 43. After the storage capacitor has had sufficient time. to charge to the desired voltage level 44, the logic circuit provides a fuser trigger command signal 45 which effects discharge of the storage capacitor as indicated at 46. to energize fuser flash lamp. This is followed by a second fuse pre-charge command signal 48 and a second fuse trigger command signal 50 to provide the second fuse flash. If more than two fuse flashes are required, the pre-charge and trigger command signals are repeated a corresponding number of times. The capacitor charge voltages illustrated provide approximately 200 and 300 joules of energy for each exposure and fuse flash, respectively.

' Referring now to'FIG. 3, a typicalschematic diagram of the circuitry associated with the flash system is shown. The pre-charge and trigger command signals from the logic circuit are fed to a group of optical isolators 52, 54, 56 and 58 ofa conventional type. Preferably, each isolator includes a light emitting diode and corresponding photosensitive transistor. For the purposes of explanation, the flash system illustrated responds to negative logic command signals. It will be appreciated that circuitry could be appropriately modified to utilize positive logic if so desirednThe power supply for the system is comprised of a power transformer, generally indicated by the numeral 60, with a primary winding 61 connected to an appropriate voltage source, such as 240 V.A.C. by way of aTriac control 64, or other switching circuit. A diode 66 and resistor 68 are connected across the secondary 62 of transformer 60. A diode 70 is connected to one line of secondary 62 to define a typical half wave rectifier. A capacitor 72 is connected to the other line of the transformer secondary and is charged up during one half of the A.C. cycle and subsequently discharged through diode 66. In effect, this arrangement provides a D.C. voltage doubler.

A main storage capacitor 74 is connected to the D.C. power by way oflines 76 and 78. By providing a capacitor 72 as a voltage doubler, approximately 3,500 V.D.C. is provided across a capacitor 74 with 1,700 V.A.C. across the transformer secondary 62. An exposure trigger transformer, generally indicated by the numeral 80, includes a primary winding 82, connected to trigger circuit 32-, and a secondary winding 84 serially connected to exposure flash lamps 16- and 18. Main storage capacitor 74 is connected in parallel with flash lamps l6 and 18 through secondary coil 84. Afuse trigger transformer, generally indicated by the numeral 86, includes primary and secondary windings 88 and 90 which are connected to the flash fuse lamp 20 and the trigger circuit ina manner similar to trigger transformer 80.

The fuse and exposure flash lamps are such that they will not flash until the associated trigger transformer has been appropriately energized. Thus, the energy stored in capacitor 74 due to the precharging operation is not discharged until such time as one of the trigger transformers is energized. Energization of either trigger transformer induces a high voltage in the corresponding secondary winding to cause the associated flash lamp to conduct, permitting the energy stored in the capacitor to be discharged through the flash lamp. This technique of triggering flash lamps, particularly of the xenon type,-is well known and a detailed discussion of such is deemed unnecessary for the purposes of this description.

In order to control the maximum voltage or charge level of the capacitor 74,, the system is provided with a level sensing circuit. This circuit includes a pair of resistors 92 and 94 which are connected across the storage capacitor to define a voltage divider which provides a charge level signal to a comparator 96 by way of line 97. When the desired charge level of capacitor 74 is reached, the output of comparator 96 goes L0 and is impressed upon the Reset input of a flip flop FFl. Preferably, FFl is comprised of a pair of cross coupled NAND gates. Thus, when the reset line goes LO, the corresponding output goes H1. This output is fed through an inverter 98, the output of which goes L0 and is impressed upon the base of transistor 100, rendering it nonconductive. The collector of transistor 100 is connected to Triac control 64 in a well known manner and effects to shutoff the control, thereby deenergizing the power supply to terminate charging of main storage capacitor 74.

The charge levels at which the DC. source is effectively disconnected from the storage capacitor may be set by a pair of adjustable potentiometers 102 and 104, which determine the exposure and fuse pre-charge levels, respectively. Potentiometer 102 is connected to the collector of transistor 106, which is base-connected to the output ofa flip flop FF2. Potentiometer 104 is similarly connected to atransistor 108, which, in turn, is base-connected to a second output of FF2. The FF2 outputs are always of opposite logic, whereby only one of the transistors 106 and 108 are conductive at the same time. Potentiometers 102 and 104 are both connected to the negative input of comparator 96 by way of line 110. Each of the potentiometers is adjusted to a desired setting corresponding to a charge level. During the exposure pre-charge mode, the setting of potentiometer 102 determines the reference level at which comparator 96 responds to terminate charging. When the system is operated in a fuse pre-charge mode, the setting of potentiometer 104 determines the charge voltage reference level.

The Set input FF2 is connected to isolator 52 by way of line 112. The Reset line of FF2 is connected to isolator 54 by way of line 114. During operation of the system in the exposure pre-charge mode, the output ofisolator 52 goes LO momentarily, causing line 112 to go L0 and the corresponding output of FF2 to switch H1, thereby turning on resistor 106. When the output of isolator 52 goes LO it is also effective to set FFl, whereby transistor 100 is rendered conductive to turn on Triac 64, to effect charging of capacitor 74. When the charge level reaches the preselected value, as determined by potentiometer 102, the output of comparator 96 goes LO, causing reset of FFl and shutoff of Triac control 64. The operation of the system during the fuse pre-charge mode is the same as that during exposure pre-charge mode explained above, except that FF2 is effective to connect potentiometer 104 into the comparator circuit to control the fuse charge level.

The exposure and fuse trigger modes of operation are controlled by trigger command signals received through isolators 56 and 58, respectively. Subsequent to exposure pre-charge, an exposure trigger command signal is provided by the logic circuit to isolator 56, which, in turn, causes line 116 to go L0 to turn off transistor 118. This causes line 120, which is connected to the collector of transistor 118, to go H1. This H1 signal is fed to a unijunction transistor 122 in trigger circuit which causes an associated SCR 124 to fire. Prior to firing of SCR 124, a capacitor 126 is charged to a predetermined level by way of transformer 128 and rectifier diode 130. Firing of SCR 124 permits discharging of capacitor 126 through the exposure trigger transformer primary 82 by way of lines 132 and 134. This initiates operation of exposure flash lamps 16 and 18. The fuse trigger mode of operation is similar to the exposure trigger mode described above, but is achieved by separate trigger circuit components including 'a unijunction transistor 136, SCR 138, and capacitor 140, connected to transistor 142 and isolator 58.

From the foregoing description, it will be appreciated that the flash system of the present invention provides a versatile, yet relatively inexpensive means for providing a flash energy for exposure and fusing. By timesharing the power supply components between the exposure and fuse operations, a single power supply may be utilized for performing two basic functions of the electrophotographic process. This results in a considerable space saving in the reproduction apparatus, together with a significant cost reduction. The versatility of the flash system is further enhanced by fixing a copy sheet with multiple flashes, each flash being of considerably less energy than the total energy required to fix an entire copy sheet.

It is not intended that the present invention be limited to the circuitry illustrated in the drawings, as such, but be appropriately modified by those skilled in the art and still achieve the time-sharing of the power supply components and the multiple flash fusing arrangement. It will also be appreciated that the disclosed multiple flash fusing arrangement which permits reduction in the size of the power supply components may be implemented by providing multiple fuse flashes, each of which irradiates the entire surface of the copy sheet, rather than fusing a section at a time. Such a multiple flash fuse arrangement may be feasible when toner is sensitive to the flashes on an additive basis.

What is claimed is:

1. In an electrophotographic reproduction apparatus for producing copies of original documents, a flash system comprising:

flash exposure means for irradiating original documents to be copied,

flash fusing means for irradiating toner images on copy material support surfaces and fusing the images thereon,

a voltage source,

flash power supply means connected to said voltage source for controlled energization of either said flash exposure means or alternately said flash fusing means, and

control circuit means operative in an exposure mode to cause said flash power supply means to energize said flash exposure means and operative in a fuse mode to cause said flash power supply means to energize said flash fusing means,

said flash power supply means including energy stor- 7 age means for storing energy for said flash exposure means and said flash fusing means, and charging circuit means for charging said storage means, said control circuit means being operative in a preexpose mode to effect operation of said charging circuit means prior to energization of said flash exposure means and operative in a pre-fuse mode to effect operation of said charging circuit means prior to each energization of said flash fusing means.

2. The system set forth in claim 1 together with sensing means for sensing the charge level of said energy storage means and providing a corresponding charge level signal to said control circuit means.

3. The system set forth in claim 2 wherein said control circuit means includes means for discontinuing charging in said pre-expose mode or said pre-fuse mode in response to said level signal reaching corresponding predetermined magnitudes, respectively.

4. The system set forth in claim 3 wherein said means for discontinuing charging includes comparison means for comparing the magnitude of said level signal with a predetermined reference level. I

5. The system set forth in claim 1 wherein the copy material support surface is comprised of a plurality of separate sections and said flash fusing means irradiates only one of said sections per flash.

6. The system set forth in claim 5 wherein said control circuit means provides a plurality of fuse mode operations to effect a series of fuse flashes corresponding to the number of said sections to be fused.

7. The system set forth in claim 6 together with means for effecting relative movement between said flash fusing means and said copy material, whereby said series of fusing flashes fixes the entire surface of said copy material.

8. The system set forth in claim 5 wherein the copy material is a generally rectangular sheet.

9. The system set forth in claim 8 together with motive means for effecting relative movement between said copy sheet and said flash fusing means,

said control circuit means including means for synchronizing each energization of said flash fusing means causing irradiation of a predetermined sin gle one of said copy sheet sections.

10. The system set forth in claim 9 wherein said control circuit means effects a series of energizations of said flash fusing means equal to the number of said copy sheet sections to be fused.

11. The system set forth in claim 10 together with flash exposure means for irradiating an original to be copied with a'radiation flash, said'control circuit means being operative in an exposure mode to cause said flash power supply means to energize said flash exposure means.

12. The system set forth in claim 1 wherein said control circuit means provides a plurality of said fuse mode operations to cause a plurality of fusing flashes for each exposure flash.

13. The system set forth in claim 12 wherein the energy of each exposure flash is in the general range of magnitude asthe energy for each fusing flash.

14. The system set forth in claim 13 wherein the energy of each of said fuse flashes is within 200% of the energy of each .of said exposure flashes.

15 The system set forth in claim 12 wherein said control circuit means causes a series of consecutive energizations of said flash fusing means for each energization of said flash exposure means. 

1. In an electrophotographic reproduction apparatus for producing copies of original documents, a flash system comprising: flash exposure means for irradiating original documents to be copied, flash fusing means for irradiating toner images on copy material support surfaces and fusing the images thereon, a voltage source, flash power supply means connected to said voltage source for controlled energization of either said flash exposure means or alternately said flash fusing means, and control circuit means operative in an exposure mode to cause said flash power supply means to energize said flash exposure means and operative in a fuse mode to cause said flash power supply means to energize said flash fusing means, said flash power supply means including energy storage means for storing energy for said flash exposure means and said flash fusing means, and charging circuit means for charging said storage means, said control circuit means being operative in a pre-expose mode to effect operation of said charging circuit means prior to energization of said flash exposure means and operative in a pre-fuse mode to effect operation of said charging circuit means prior to each energization of said flash fusing means.
 2. The system set forth in claim 1 together with sensing means for sensing the charge level of said energy storage means and providing a corresponding charge level signal to said control circuit means.
 3. The system set forth in claim 2 wherein said control circuit means includes means for discontinuing charging in said pre-expose mode or said pre-fuse mode in response to said level signal reaching corresponding predetermined magnitudes, respectively.
 4. The system set forth in claim 3 wherein said means for discontinuing charging includes comparison means for comparing the magnitude of said level signal with a predetermined reference level.
 5. The system set forth in claim 1 wherein the copy material support surface is comprised of a plurality of separate sections and said flash fusing means irradiates only one of said sections per flash.
 6. The system set forth in claim 5 wherein said control circuit means provides a plurality of fuse mode operations to effect a series of fuse flashes corresponding to the number of said sEctions to be fused.
 7. The system set forth in claim 6 together with means for effecting relative movement between said flash fusing means and said copy material, whereby said series of fusing flashes fixes the entire surface of said copy material.
 8. The system set forth in claim 5 wherein the copy material is a generally rectangular sheet.
 9. The system set forth in claim 8 together with motive means for effecting relative movement between said copy sheet and said flash fusing means, said control circuit means including means for synchronizing each energization of said flash fusing means causing irradiation of a predetermined single one of said copy sheet sections.
 10. The system set forth in claim 9 wherein said control circuit means effects a series of energizations of said flash fusing means equal to the number of said copy sheet sections to be fused.
 11. The system set forth in claim 10 together with flash exposure means for irradiating an original to be copied with a radiation flash, said control circuit means being operative in an exposure mode to cause said flash power supply means to energize said flash exposure means.
 12. The system set forth in claim 1 wherein said control circuit means provides a plurality of said fuse mode operations to cause a plurality of fusing flashes for each exposure flash.
 13. The system set forth in claim 12 wherein the energy of each exposure flash is in the general range of magnitude as the energy for each fusing flash.
 14. The system set forth in claim 13 wherein the energy of each of said fuse flashes is within 200% of the energy of each of said exposure flashes.
 15. The system set forth in claim 12 wherein said control circuit means causes a series of consecutive energizations of said flash fusing means for each energization of said flash exposure means. 